Abnormal bicarbonate secretion has long been recognized as a key component of cystic fibrosis (CF) pancreatic dysfunction, but has only recently been investigated as a component of CF lung disease. The submucoal glands of the lungs are responsible for secretion of a complex airway surface liquid (ASL) that lines the airway epithelium and plays a significant role in mucociliary clearance. The serous cell is the predominant cell type of the submucosal gland and the predominant site of cystic fibrosis transmembrane conductance regulator (CFTR) expression. The Calu-3 cell, an immortalized serous cell line, is therefore a good model for the study of the physiology of ASL production and regulation. This proposal is divided into two complementary aims. The first aim is to use microelectrode measurements to establish the transport physiology of bicarbonate entry on a sodium-bicarbonate cotransporter, and then to use short, inhibiting RNA technology to determine the identity of the sodium-bicarbonate cotransporter. The second aim is to use short, inhibitory RNA technology to knock-down CFTR and to use these knock-down cell lines in Ussing chamber experiments and microelectrode experiments to test the hypothesis that CFTR is the apical bicarbonate channel.